Leishmania donovani, the causitive agent in visceral leishmaniasis (Kala-azar), possesses a very potent acid phosphatase (ACP) that is located on the outer surface of the promatigote form. A major goal of the proposal is to isolate the ACP in pure form in amounts sufficient to permit certain physical-chemical and kinetic characterizations that include: molecular weight, carbohydrate and amino acid composition, subunit size and number, substrate specificity (including phosphoproteins) and sensitivity to potent ACP inhibitors of the heteropoly molybdenum class. Our goal is to identify effective inhibitors of L. donovani ACP that do not inactivate mammalian phosphatases. Inhibitory compounds with these properties will be tested in an in vitro monocyte-derived macrophage system to determine if they have antileishmanial activity. This project will provide new information about the properties of the unusual ACP in the sandfly-borne human parasite, L. donovani and may lead to the identification of a new class of compounds with therapeutic potential.